Fixed `HTTPTest.QueryEncodeDecode`.
Fixed `HTTPTest.QueryEncodeDecode`.

This commit fixes MESOS-8551.

Stout's `hashmap` is a wrapper around `std::unordered_map`. The
Standard Template Library places no restriction on the iteration order
for the elements of an `unordered_map`. Because of this, different
implementations of `unordered_map` can and do iterate the elements in
different orders. The implementation of `http::query::encode` uses the
iteration order of `std::unordered_map` to encode the elements.

The test case has two items in the `unordered_map`, which makes it
possible for `encode` to return either of two different orders. The
solution in this fix tests that the return value from `encode` matches
either of the possible orders. This was not previously an issue
because the implementations of GCC and Clang were consistent; however,
MSVC happens to encode in the order. This is not incorrect, just
different.

This patch also added a second test to ensure that either possible
output of `encode` would correctly decode.

Review: https://reviews.apache.org/r/65577/

gsantovena/mesos,asamerh4/mesos,andschwa/mesos,reneploetz/mesos,abudnik/mesos,gsantovena/mesos,andschwa/mesos,kaysoky/mesos,Gilbert88/mesos,asamerh4/mesos,dforsyth/mesos,andschwa/mesos,reneploetz/mesos,andschwa/mesos,abudnik/mesos,kaysoky/mesos,jpeach/mesos,andschwa/mesos,abudnik/mesos,chhsia0/mesos,abudnik/mesos,Gilbert88/mesos,gsantovena/mesos,andschwa/mesos,Gilbert88/mesos,reneploetz/mesos,reneploetz/mesos,chhsia0/mesos,jpeach/mesos,dforsyth/mesos,chhsia0/mesos,jpeach/mesos,dforsyth/mesos,Gilbert88/mesos,asamerh4/mesos,kaysoky/mesos,abudnik/mesos,gsantovena/mesos,kaysoky/mesos,jpeach/mesos,dforsyth/mesos,kaysoky/mesos,gsantovena/mesos,reneploetz/mesos,chhsia0/mesos,gsantovena/mesos,dforsyth/mesos,dforsyth/mesos,kaysoky/mesos,Gilbert88/mesos,chhsia0/mesos,abudnik/mesos,kaysoky/mesos,jpeach/mesos,asamerh4/mesos,asamerh4/mesos,abudnik/mesos,reneploetz/mesos,Gilbert88/mesos,jpeach/mesos,reneploetz/mesos,chhsia0/mesos,chhsia0/mesos,Gilbert88/mesos,asamerh4/mesos,andschwa/mesos,dforsyth/mesos,asamerh4/mesos,jpeach/mesos,gsantovena/mesos